Method for solidifying radioactive waste

Abstract

PCT No. PCT/JP84/00250 Sec. 371 Date Jan. 16, 1985 Sec. 102(e) Date Jan. 16, 1985 PCT Filed May 18, 1984 PCT Pub. No. WO84/04624 PCT Pub. Date Nov. 22, 1984.A process for solidifying radioactive wastes, which comprises adding, to pellet or dissolved radioactive wastes, an alkali metal silicate as a filler, silicic acid, carbonic acid or an alkaline earth metal or polyvalent metal salt thereof as a hardener, and cement as an absorbent for absorbing water to be released with the progress of the reaction and, if necessary, water and mixing and solidifying the resulting mixture to thereby prevent deterioration of water-proofness due to precipitation of readily soluble salts on the surface of a solidified substance.

We claim: 
     
       1. A method for solidifying radioactive waste which comprises mixing the radioactive waste with a solidifying agent prepared by mixing an alkali metal silicate as a solidifying filler; an inorganic compound as a hardening agent for reacting with said alkali metal silicate; cement as a water absorbent for absorbing liberated water generated in the course of the hardening reaction between said alkali metal silicate and said inorganic compound; and water; wherein said inorganic compound contains an ion able to bind with an alkali metal in said alkali metal silicate to form a low-solubility salt, said inorganic compound being a compound of a polyvalent metal ion selected from the group consisting of Ca 2+ , Mg 2+ , Al 3+ , and Fe 3+  or an H +  ion and an ion selected from the group consisting of TaO 3   - , AlF 6   3- , NbO 3   - , SiF 6   2- , SiO 3   2- , BeF 4   2- , B 4  O 7   2- , F - , IO 4   - , ClO 4   - , BF 4   -  and ReO 4   - .   
     
     
       2. A method for solidifying radioactive waste according to claim 1, wherein the content of said inorganic compound in the solidifying agent is not less than 3% by weight but not greater than 50% by weight. 
     
     
       3. A method for solidifying radioactive waste according to claim 1, wherein the content of said cement in the solidifying agent is not less than 3% by weight but not greater than 35% by weight. 
     
     
       4. A method for solidifying radioactive waste according to claim 1, wherein the content of said water in the solidifying agent is not less than 15% by weight but not greater than 40% by weight. 
     
     
       5. A method for solidifying radioactive waste according to claim 1, wherein said alkali metal silicate is selected from the group consisting of sodium silicate, potassium silicate and lithium silicate. 
     
     
       6. A method for solidifying radioactive waste according to claim 1, wherein said inorganic compound is CaSiO 3 . 
     
     
       7. A method for solidifying radioactive waste according to claim 1, wherein said alkali metal silicate is sodium silicate. 
     
     
       8. A method for solidifying radioactive waste according to claim 7, wherein said inorganic compound is CaSiO 3 . 
     
     
       9. A method for solidifying radioactive waste according to claim 2, wherein the content of said alkali metal silicate as a solidifying filler in the solidifying agent is about 37.5% by weight. 
     
     
       10. A method for solidifying radioactive waste according to claim 3, wherein the content of said alkali metal silicate as a solidifying filler in the solidifying agent is about 37.5% by weight. 
     
     
       11. A method for solidifying radioactive waste according to claim 4, wherein the content of said alkali metal silicate as a solidifying filler in the solidifying agent is about 37.5% by weight. 
     
     
       12. A method for solidifying radioactive waste according to claim 1, wherein the viscosity of the solidifying agent before it is hardened is less than about 3,000 cP. 
     
     
       13. A method for solidifying radioactive waste according to claim 1, wherein the radioactive waste and the solidifying agent are mixed in approximately equal amounts by weight. 
     
     
       14. A method for solidifying radioactive waste according to claim 1, wherein the content of said inorganic compound in the solidifying agent is not less than 3% by weight but not greater than 50% by weight; the content of said cement in the solidifying agent is not less than 3% by weight but not greater than 35% by weight; the content of said water in the solidifying agent is not less than 15% by weight but no greater than 40% by weight; and the content of said alkali metal silicate in the solidifying agent is about 37.5% by weight. 
     
     
       15. A method for solidifying radioactive waste according to claim 8, wherein the content of said inorganic compound in the solidifying agent is not less than 3% by weight but not greater than 50% by weight; the content of said cement in the solidifying agent is not less than 3% by weight but not greater than 35% by weight; the content of said water in the solidifying agent is not less than 15% by weight but not greater than 40% by weight; and the content of said alkali metal silicate in the solidifying agent is about 37.5% by weight.